Tested each of diode pair fch20u10 with analog ohm-meter:
directly-open but with bigger direct voltage conducts, inversely-
resistance of 40 ohms!
but I suspect it is ok or not because tested an ok mur1620 and it
showed 100ohms
I guess those fast power diodes should not show inverse resistance of
Kohms?

On Thu, 16 Dec 2010 09:09:27 -0800, mynick wrote:

Tested each of diode pair fch20u10 with analog ohm-meter: directly-open
but with bigger direct voltage conducts, inversely- resistance of 40
ohms!
but I suspect it is ok or not because tested an ok mur1620 and it
showed 100ohms
I guess those fast power diodes should not show inverse resistance of
Kohms?

Schottky diodes have a very low forward voltage drop. Normal silicon
is .6 - 1.7 vdc while Schottky is .15 - .45vdc.




--
Live Fast, Die Young and Leave a Pretty Corpse

On Thu, 16 Dec 2010 17:27:12 +0000 (UTC), Meat Plow
wrote:

On Thu, 16 Dec 2010 09:09:27 -0800, mynick wrote:

Tested each of diode pair fch20u10 with analog ohm-meter: directly-open
but with bigger direct voltage conducts, inversely- resistance of 40
ohms!
but I suspect it is ok or not because tested an ok mur1620 and it
showed 100ohms
I guess those fast power diodes should not show inverse resistance of
Kohms?

Schottky diodes have a very low forward voltage drop. Normal silicon
is .6 - 1.7 vdc while Schottky is .15 - .45vdc.

It could be that your meter is not placing a high enough reverse
voltage bias to completely turn off the junction.

On Dec 16, 9:09*am, mynick wrote:
Tested each of *diode pair fch20u10 with analog ohm-meter:
directly-open but with bigger direct voltage conducts, inversely-
resistance of 40 ohms!

The usual failure mode of high current rectifiers is short
circuit (i.e. large reverse conduction). If this is out-of
circuit, probably the diode is dead. A 'real' test, though,
would require known voltages and currents, not just
the 'ohms' value (a ratio of unknown voltage and current,
whatever the meter manufacturer thought was best).
If your resistance scale measures at microamps, the
milliamp leakage specification might not be violated,
but you'd never know it.

Is this a stud rectifier? If it is, are you sure the stud is the cathode?
Some types come both ways.

On Dec 17, 10:31*pm, "William Sommerwerck"
wrote:
Is this a stud rectifier? If it is, are you sure the stud is the cathode?
Some types come both ways.

common cathode

mynick wrote:

On Dec 17, 10:31 pm, "William Sommerwerck"
wrote:
Is this a stud rectifier? If it is, are you sure the stud is the cathode?
Some types come both ways.

common cathode


Common cathode only applies to multiple diodes in one package, with
the cathodes tied together.

Reverse polarity stud mount diodes typically have the same part
number, with 'R' appended to the end.

--
For the last time: I am not a mad scientist, I'm just a very ticked off
scientist!!!